Chapter 14 - Alcohols Flashcards
What’s the functional group of alcohols?
-OH
Are alcohols polar?
Yes, they have polar O-H bond because of difference in electronegativity of oxygen and hydrogen atoms
What is volatility?
Measure of how easy a liquid is converted into a gas
Why do alcohols have a lower volatility than alkanes?
Have a higher boiling point
Why are the boiling points of alcohols greater than the boiling points of alkanes?
Strong hydrogen bonds between the O-H (polar) groups.
This requires more energy than overcoming the weaker london forces in alkanes.
Why are alcohols soluble in water?
Form hydrogen bonds with water.
between polar OH groups
Do alcohols get more or less soluble in water as the carbon chain increases in size?
-Less soluble.
As influence of the -OH group becomes relatively smaller
What are the 3 ways alcohols are classed?
- Primary
- Secondary
- Tertiary
What are primary alcohols?
- Alcohol where the -OH group is attached to a carbon atom that is attached to one alkyl group (and 2 hydrogens).
- e.g. ethanol
What is a secondary alcohol?
- Alcohol where OH groups is attached to a carbon atom that is attracted to one hydrogen and 2 alkyl groups
- e.g. propan-2-ol
What is a tertiary alcohol?
Alcohol where OH group is attracted to a carbon atom that is attracted to no hydrogen atoms and 3 alkyl groups.
e.g. 2-methylpropan-2-ol
What is complete combustion?
Combustion in plentiful supply of oxygen
What are the products formed in complete combustion of an alcohol?
carbon dioxide + water
Give the equation for complete combustion of ethanol
C2H5OH(l) + 3O2(g) -> 2CO2(g) + 3H2O(l)
Does the quantity of heat released per mole increase or decrease in combustion for longer chain alcohols?
Increases
What is the oxidising agent mixture used for oxidising alcohols?
Solution of potassium dichromate (VI), K2Cr2O7, acidified with dilute sulphuric acid, H2SO4
What does oxidising a primary alcohol by gently heating distillation form?
Aldehyde
Describe process of oxidising a primary alcohol to form an aldehyde
Gently heat primary alcohol with potassium dichromate and sulphuric acid (oxidising agent) in distillation apparatus (volatile components can escape) to form aldehyde, which is the most volatile component (boils at lower temperature).
Write the equation for oxidation of butan-1-ol
CH3CH2CH2CH2OH + [O] -> CH3CH2CH2CHO + H2O
What does (oxidising) heating a primary alcohol under reflux form?
Carboxylic acid
Describe the process of oxidising a primary alcohol to form a carboxylic acid
Heat primary alcohol with acidified potassium dichromate under reflux.
This forms an aldehyde but stays in reaction vessel with oxidising agent forming carboxylic acid. (volatile components can’t escape)
Write equation for oxidation of primary alcohol, butan-1-ol, to form a carboxylic acid
CH3CH2CH2CH2OH + 2[O] -> CH3CH2CH2COOH + H2O
What do secondary alcohols form when oxidised?
ketones
What colour does a solution containing orange dichromate ions turn when reduced?
Green
Describe oxidation of a secondary alcohol to form a ketone
Heat alcohol mixed with acidified potassium dichromate under reflux, forming ketone
Give equation for oxidation of propan-2-ol
CH3CHOHCH3
What do tertiary alcohols form when oxidised?
They don’t oxidise
What is dehydration of an alcohol? What is the product of this? What type of reaction is this?
- When a water molecule is removed from a starting material (alcohol)
- Forms an alkene
- Elimination
Describe the process of dehydration of an alcohol
Alcohol heated under reflux in presence of an acid catalyst such as concentrated phosphoric acid, H3PO4. Producing an alkene
Give equation for dehydration of cyclohexanol
(CH2)5CHOH -> C6H12 + H20
Describe the process of forming a haloalkane to from an alcohol
Alcohol heated under reflux with sulphuric acid and sodium halide.
Sulphuric acid reacts with sodium halide to form hydrogen halide, which reacts with alcohol to form haloalkane.
What kind of reaction is the formation of haloalkane from an alcohol?
Substitution
Write the overall equation for reaction of propan-2-ol with H2SO4 and NaBr
CH3CHOHCH3 +NaBr +H2SO4 -> CH3CHBrCH3 + NaSO4 +H2O
What is formed when a carboxylic acid and an alcohol are heated under reflux in presence of acid catalyst
Ester
How do you name an ester?
Use alcohol stem and put -yl at the end and use carboxylic acid stem and add -oate.
e.g. methyl ethanoate
What is required for fermentation, producing an alcohol?
Yeast and aqueous solution of sugar (glucose)
What is produced in fermentation of glucose?
Carbon dioxide and ethanol
Give equation for fermentation of glucose?
C6H12O6(aq) -> 2C2H5OH(aq) + 2CO2(g)
